One of the authors of the paper, Professor Ian Roberts, told the BBC: "When people think about environmental sustainability, they immediately focus on population. Actually, when it comes down to it, it’s not how many mouths there are to feed, it is how much flesh there is on the planet."

"If every country in the world had the same level of fatness that we see in the USA, in weight terms that would be like an extra billion people of world average body mass," he added.

Roberts said health campaigns and urban design that promotes walking or cycling were among the best ways to tackle the problem, which was primarily caused by sedentary modern lifestyles.

“We do not move our bodies so much but we are biologically programmed to eat,” he told the Daily Telegraph. "We often point the finger at poor women in Africa having too many babies. But we've also got to think of this fatness thing; it's part of the same issue of exceeding our planetary limits."